Metformin blocks migration and invasion of tumour cells by inhibition of matrix metalloproteinase-9 activation through a calcium and protein kinase Cα-dependent pathway: phorbol-12-myristate-13-acetate-induced/extracellular signal-regulated kinase/activator protein-1

Background and purpose: Population studies have revealed that treatment with the anti-diabetic drug metformin is significantly associated with reduced cancer risk, but the underlying mode of action has not been elucidated. The aim of our study was to determine the effect of metformin on tumour invasion and migration, and the possible mechanisms, using human fibrosarcoma HT-1080 cells. Experimental approach: We employed invasion, migration and gelatin zymography assays to characterize the effect of metformin on HT-1080 cells. Transient transfection assays were performed to gene promoter activities, and immunoblot analysis to study its molecular mechanisms of action. Key results: Metformin inhibited migration and invasion by HT-1080 cells at sub-toxic concentrations. In these cells, metformin also suppressed phorbol-12-myristate-13-acetate (PMA)-enhanced levels of matrix metalloproteinases-9 (MMP-9) protein, mRNA and transcription activity through suppression of activator protein-1 (AP-1) activation. In addition, metformin strongly repressed the PMA-induced phosphorylation of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and protein kinase C(PKC)alpha, whereas the phosphorylation of p38 mitogen-activated protein kinase was not affected by metformin. Metformin decreased the PMA-induced Ca2+ influx. Furthermore, treatment with an intracellular Ca2+ chelator (BAPTA-AM) or a selective calmodulin antagonist (W7) markedly decreased PMA-induced MMP-9 secretion and cell migration, as well as activation of ERK and JNK/AP-1. Conclusions and implications: Metformin inhibited PMA-induced invasion and migration of human fibrosarcoma cells via Ca2+-dependent PKC alpha/ERK and JNK/AP-1-signalling pathways. Metformin therefore has the potential to be a potent anti-cancer drug in therapeutic strategies for fibrosarcoma metastasis.